Active pharmaceutical ingredients showing an ester, amide or thioester functionality are often sensitive to moisture and frequently show chemical incompatibility with a wide range of commonly used pharmaceutical excipients, thus typical formulation approaches such as lipid based drug delivery systems can not be considered. Incorporating the drug substance into a hygroscopic polymer matrix can be critical due to chemical as well as physical stability. The sorption of moisture by excipients in solid dosage forms can lead to considerable stability problems when the contained active pharmaceutical is instable in water due to the presence of a hydrolysis sensitive functional group. Though theoretically hygroscopic polymers are capable to bind moisture in the formulation, thus protecting the active pharmaceutical ingredient from hydrolysis, a fairly high amount of polymer is needed to achieve this what usually leads to capping or cracking of the immediate-release tablet formulation. Thus, it is usually imperative to prevent moisture sorption during storage by both, a suitable formulation and primary packaging.